1. Field of the Invention
This invention relates to an electrochemical device, and in particular relates to an electrochemical device having a pair of fixed collecting plates arranged on both sides of a stacked member, which is the main body, in the stacking direction.
2. Description of the Related Art
In recent years there has been much interest in electrochemical devices such as electric double-layer capacitors for use as batteries which afford comparatively large capacities in a compact size and with light weight. An electric double-layer capacitor does not utilize a chemical reaction as in the case of ordinary secondary batteries, but instead is a battery type which directly accumulates charge on electrodes, and so has the feature of enabling extremely rapid charging and discharging. Applications which exploit this feature are envisioned in, for example, backup power supplies for portable equipment (compact electronic equipment) and similar, and as auxiliary power supplies for electric vehicles and hybrid vehicles; and various studies are being conducted to improve the performance of such batteries.
As the basic construction of an electric double-layer capacitor, a plurality of collectors in which polarizable electrode layers are formed, and a plurality of separators which separate adjacent polarizable electrode layers, are arranged in alternation; the interior of this stacked member is filled with an electrolytic solution. However, in an electric double-layer capacitor which uses a carbon material or similar as the material of the polarizable electrode layers, there is the property that upon charging the polarizable electrode layers expand by approximately 10% in the thickness direction. Consequently the problem arises that when a voltage is applied, the electric double-layer capacitor expands in the stacking direction.
When such expansion occurs, not only is stress applied to the housing due to the deformation, but there is the further problem that the internal resistance of the electric double-layer capacitor increases. Consequently a method is adopted in which a pair of fixed collecting plates or similar are provided in the stacking direction of the stacked member which is the main body of the capacitor, and by this means expansion is suppressed (see Japanese Patent Laid-open No. 3-80519, Japanese Patent Laid-open No. 7-263029, and Japanese Patent Laid-open No. 11-73937).